1. Field of the Invention
The present invention relates to a biological detecting system and a fingerprint collating system employing that biological detecting system.
2. Description of the Related Art
The increasing growth and use of information systems has raised a problem of how to maintain the security of such systems. Currently, as one means of identifying a person allowed to use the information system, an ID card is employed, but the ID card is easily lost or stolen. Also, it is relatively simple to obtain a code number of the ID card using known information about the owner of the card. Accordingly, as a substitute for the ID card, use is made of fingerprints, since these are different for each person and do not change during a person's life time, and therefore, various simple individual collating apparatuses for fingerprints and fingerprint collating system have been developed. In the fingerprint collating systems, a fingerprint is handled as an image, and therefore, in this kind of system an input apparatus must be provided for converting a detected image of the fingerprint into image data.
FIG. 32 is a schematic view of a typical arrangement of a fingerprint image input apparatus. In the operation of this apparatus, a finger 70 is placed in contact with a transparent member 71, and the finger is illuminated as indicated by the arrows. Among light scattered from ridges (projecting portions) of a fingerprint, components (indicated by dotted lines) thereof that are totally reflected by interfaces of the transparent member are collected by an optical system 72 to form an image, and a photodetector 73 such as a charge-coupled-device (CCD) is used to obtain an image of the ridge pattern.
Nevertheless, a replica having the same irregular pattern as the pattern of a previously registered fingerprint can be produced, and can be used for the fingerprint collation, and thus the system security is not fool-proof. Accordingly, there is a need for a mechanism capable of judging whether the irregular pattern of a sample in contact with the fingerprint image input apparatus originates from a genuine finger (a biological object) or from a replica (a non-biological object), i.e., a biological detecting mechanism is required.
An example of a conventional biological detecting system is shown in FIG. 33. This first prior art example is an optical system utilizing a phenomenon that an amount of light transmitted through a human body will be changed by a pulsation of the human body. Namely, the transparency to light of a finger 80 under a red light from a light source 81 is changed in the same cycle as that of the pulsation of the human body, and this cycle of change of the transparency is detected by a photodetector 82 to determine whether or not the sample is a biological object.
Another system (second prior art example) is shown in FIG. 34. This is an electrical system utilizing a difference between the resistance value of a finger and the resistance value of a replica. On a surface (a hatched portion), with which contact is made by a finger, are arranged transparent electrodes 91 and 92 for measuring a resistance value of the finger and the measured value is compared with a preset resistance value of a replica to determine whether or not the finger is a biological object. In this case, a fingerprint image input apparatus receives an image of the fingerprint to be compared and judged, together with images of the electrode patterns.
According to the first prior art example, a time of several seconds or more is needed to detect the pulsation, and therefore, to perform a biological detection, the finger must be kept in contact with the fingerprint image input apparatus for the time necessary to detect the pulsation. This is disadvantageous in that, if the contact by a sample is broken before that time has elapsed, it is impossible to determine whether or not the sample is a biological object.
The second prior art requires only a short time for carrying out the biological detection, but the electrode patterns may disturb an image of the fingerprint. Therefore, although the biological detection can be carried out without hindrance, it may be difficult to carry out the fingerprint collation after the biological detection is effected. Further, the resistance value of a human finger may vary in accordance with the pressure applied and the presence of perspiration on the skin. To cope with this problem, the allowable resistance value must be very large, but if the allowable resistance value is large, a difference between a reference value and the resistance value of the replica becomes smaller, and thus it becomes difficult to carry out the comparison and determination in the biological detection. Also, it would be possible to provide a replica with the same resistance value as a human finger, and thus the security of system will be compromised.